Apparatus for coating the inside surfaces of tubular vitreous envelopes



A. H. LAIDIG EI'AL 2,449,783 APPARATUS FOR COATING THE INSIDE SURFACES Sept. 21, 1948.

A 0? TUBULAR VITREOUS ENVELOPES 3 Sheets-Sheet 1 Filed Se pt. so. 1943 Hwz we m

m A HR Sept. 1948- A. H. LAIDIG ETAL APPARATUS FOR COATING THE INSIDE SURFACES 0F TUBULAR VITREOUS ENVELOPES Filed Sept. so. 194

3 Sheets-Sheet 2 INVENTORS H H. 1 9/0/6 BY W9 ATTORNEY p 1943- AJH. LAIDIG Erin. 2,449,783

I APPARATUS FOR' COATING THE INSIDE SURFACES OI" TUBULAR VI'I'REOUS ENVELOPES Filed Sept so, 1943 3 Shoots-Sheet 3 M MI/m n54:

W MW

ATTORNEY Patented Sept. 21, 1948 APPARATUS FOR COATING THE INSIDE SURFACES OF TUBULAR VITREOUS EN- VELOPES Alfred H. Laidig, Bloomfield, and Frederick T. May, Verona, N. J asslgnors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 30, 1943, Serial No. 504,372

9 Claims. 1

This invention relates to coating vitreous envelopes, and, more particularly, the inside surfaces of elongated tubes such as employed for fluorescent lamps and the like.

The principal object of our invention, generally considered, is to automatically coat the inside surfaces of vitreous envelopes uniformly and in an economical and convenient manner, with safety means provided to avoid overflow of the coating material. 7

Another object of our invention is to provide control means, including such detectors as photocells, for shutting off the supply of coating material at the proper time and causing it to drain out of the envelope being coated.

A further object of our invention is the provision of apparatus for coating the inside surfaces of elongated vitreous envelopes comprising a carrier for a plurality of said envelopes, means for either successively indexing said envelopes or moving them at a predetermined rate of speed,

a reservoir of coating material, a flexible con- VIIVII of Fig. 6, in the direction 01' the arrows.

necting tube from said reservoir, means for causing said tube to temporarily connect with one or more of said envelopes, a source of compressed air, means connecting said source to said reservoir, and means for admitting compressed air to said reservoir above the coating material to, at the proper time, force said coating material into one or more of the vitreous envelopes, means being provided to at the proper time shut off and drain the coating material from said envelope, or envelopes, thereby preventing overflow and insuring that the coating thereon will be uniform.

Other objects and advantages of th invention, relating to the particular arrangement and construction of the various parts, will become apparent as the description proceeds.

In the drawings,

Fig. 1 is a fragmentary plan of mechanism embodying our invention.

Fig. 2 is a fragmentary vertical sectional view on the line II-II of Fig. 1, in the direction of the arrows, and on a larger scale.

Fig. 3 is a view corresponding to Fig. 1 but showing another embodiment of our invention.

Fig. 4 is a fragmentary vertical sectional view on the line IV-IV of Fig. 3, in the direction of thearrows, and on a larger scale.

Fig. 5 is a fragmentary vertical sectional view on the line V'-V of Fig. 4, in the direction of the arrows.

Fig. 6 is a view corresponding to Fig. 2, but

showing a further embodiment of our invention. Fig. 7 is a horizontal sectional view on the line Fig. 8 is an elevational view, on a small scale, of part of the apparatus of the form of Figs. 6 and 7.

A purpose of the present invention is to obviate the necessity of having an operator watch the rise of the liquid, of the fluorescent or other mixture, in an envelope being coated, in order to shut off the air pressure as soon as the liquid reaches the upper end of said envelope. Such an operation is dependent solely on the constant alertness and good judgment of the operator, as each envelope must be completely coated during one continuous rise and fall of the liquid in order to achiev the best results.

Referring now to the drawing in detail, like parts being designated by like reference characters, and first considering the embodiment of our invention illustrated in Figs. 1 and 2, there is shown a coating machine comprising a conveyor ll having a plurality of clips l2 between which are. held elongated light-pervious vitreous envelopes or tubes I3, such as those employed in the manufacture of fluorescent lamps, that is, they may be generally-cylindrical hollow tubes open at top and bottom. The conveyor I I rotates and is adapted to periodically index or stop after it has turned a distance equal to the circumferential distance between adjacent tubes, times the number of tubes handled at once, which in the present embodiment is one.

In addition to the clips l2, there are in the present embodiment sockets It for holding the tubes l3, comprising supporting brackets I 5 with upstanding and depending threaded cylindrical portion I6 and I1 receiving rubber packing members I8 and 19-, held in place as by means of hollow nuts 2| and 22. Each nut 2| may be so adjusted that the packing IB enclosed is just right to hold the lower end of the associated tube l3, making a fluid tight connection therewith.

Associated with the conveyor II is a table, bench or other support 23, from which projects a standard or pedestal 24 carrying a bracket 25, on which is pivotally-mounted a bell crank lever 26, one arm 3| of which is normally urged toward the conveyor by a coil spring 2'l,.so as to release the lower contact element 28 from its cooperating element 29 and open a control circuit when there is no tube in place. When, however, the tube i3 is in place, as illustrated in Fig. 2, it engages the inclined arm 3| of said lever 28 and causesthe adjustable set screw 32 thereof to push the lower contact element 28 against its associated element 28 to close the control circuit/and put the appalaws in condition for operation.

The standard 24 also has another bracket 88 which adiustably carries a housing 84 containing an upper photocell or similar sensitive eledirecting horizontal beams of light to the photocells 85 and 88. The upper beam is at approxe imately the end oif the indexed tube l8 while the lower beam is enough therebelowto slow the flow V of coating fluid sumciently so it may be accurately stopped at theupper end of the indexed tube.

A source of power 4 l connects through switch 42 and lines 48 and to the lamps 81 and 88. It

also connects to amplifier and relay circuit 45, for the "slow up operation, through lines 48 and 81 and 88, and the controlling photocells 85 and 88, the contacts 28 and 28 being engaged as the envel indexes, so as to energize the control circui opening the "air escape" valve 12 and fully opening the "slow up" valve- 84.

Atthe same time, turning of the cam 85, as by means of its power operated shaft 81, brings the plug 88 into engagemeht with the gasket l8 to allow the coating fluid 88 to be forced through the flexible tube 88 from the reservoir 81, by means of the compressed air through .pipe 85, up into the tube l'lfor coating the interior thereof. It is, of course, understood that the stirrer 88 is during the operation working to keep the coating fluid in proper condition;

. til it intercepts the light beam to the lower photo- 41, said circuit being, in turn, connected through I lines 48, 48, 5|, 52, 58 and 54 to-the photocell 88.

Said amplifier and relay circuit 45 is also connected to slow up" solenoid 55 through lines 58,

, 51, 58-, 58, contacts 28-and 28, lines 8|, 82 and 88, which solenoid controls the slow up valve 84 to nearly shut off the supply of air at accurately regulated pressure from compressed air source through regulator 88 and pipe 85, when the 1 coating fluid 88 from reservoir 81, to which said pipe is connected, rises to a point where it intercepts the beam of light to the slow up photocell88; The coil spring 88 normally nearly closes valve 84 by movingthe handle 88 until it engages an adjustable stop 1| when the power is cut off. as when there is no envelope I8 in engagement with the bell crank lever arm 8|, or the coating fluid and coating on the envelope cuts off the flow of light to the photocell 88.

An air escapeor"sh ut of! three way valve 12 is provided and disposed between the valve 84 and reservoir 61,- so as to admit compressed air to the reservoir 81 when: open and exhaust it therefrom when closed. when the coating fluid 88, after'being retarded, rises to the upper end 84 and 85. The handle 85 of the valve 12 is normally urged into closed position by coil spring 81. The coating fluid 88 in the reservoir 81 is kept in uniform condition by a stirrer 88, desirably operated by an electric motor 88. It feeds into the indexed envelope l3 through socket |4- from pipe-88 dipping thereinto, flexible tube 88, and pipe 8|, carried by angular lever 82 pivoted as indicated at 88 and carrying a roller 84 normally engaged by operating cam 85. The upper end of the pipe 8i carries a plug 88 which fits the rubber gasket l8 oi the socket l4 when urged into engagement therewith by the cam 85, so as to temporarily connect with the indexed envelope I 3 for coating purposes, as illustrated in Fig. 2.

The operation of the apparatus previously described is as follows: The conveyor II is caused to rotate intermittently, successively bringing,

in the present embodiment, one tube or envelope l8 into position so that the upper end thereof lies between the source of light, provided by the lamps cell 88, causing de-energization of the solenoid 55 and partial closing of the slow up" valve 84, as

allowed by the setting of the stop 1i, whereupon it proceeds at a slower rate, until it intercepts the light beam to the upper photocell 85, causing de-energlzation of the solenoid 18 and closing of the air escape" valve 12, cutting oil. the air supply, releasing the air above the fluid 88 in reservoir 81, and allowing said fluid in the indexed envelope l8 to flow back into the reservoir through the flexible tube 88. The coating adhering to the envelope prevents the beams of light fromreenergizing the control circuits until said envelope has moved on and the next one indexed. After this coating-fluid return has 00'- curred, continued operationof the cam 85 will cause the plug 88 to drop away from the socket gasket l8, allowing the coated envelope to move on with the conveyor II, the control circuits being kept deenergized by opening of the contacts 28 and 28 until the next tube is indexed. The socket gasket l8 of the next tube I8, as indexed,

is engaged by plug 85, and the process repeated.

Referring now to the embodiment of our invention illustrated in Figures 3, 4 and 5, there is shown a coating machine comprising a conveyor Il having a plurality of clips l2", between which are held elongated vitreous envelopes or tubes I8, such as those employed in the manufacture of fluorescent lamps, as in the flrst embodiment. The conveyor Il rotates but does not index. The present embodiment is, therefore, to provide for coating the inside surfaces of such envelopes while they are rotating with the conveyor instead of while stationary.

The lower end of each tube l8 fits its socket I4 which may correspond with the sockets l4 of the preceding embodiment 'and be held in a supporting bracket l5 with upstanding and depending threaded cylindrical portions receiving rubber packing members, and held in place by standard 24* has a movable bracket 83 which adjustably carries housing members 84 and 48 containing, respectively, a source of light and photocells corresponding with the cells 35 and 88 of the preceding embodiment. The shield 88 is provided with upper slits II and lower slits I82 for, respectively, transmitting an upper horizontal beam of light to the upper photocell and flexible tube 88 and pipe carried by the angular lever 82", pivoted as indicated at 30, and carrying roller 84 normally engaged by operating cam The upper end of the lever-carried pipe has a plug 36 which normally fits the lower rubber gasket oi the adjacent socket I 4, when urged into engagement-therewith by the spring II'I, upon release by the cam 80, so as to temporarily connect with an envelope I3 for coating Registry of the plug 00 and associated gasket is insured by, a stud I03 on lever 32 engaging indexing aperture I04 in bracket Iii, so thatthe lever 9i. and its supporting element I00, move about a vertical pivot (not shown) which is coaxial with the conveyor II Thus, the lever 92-" and its plug 90 are carried along in engagement with the socket I4, until released by action with the cam 95', such movement being against the force of the return spring I08, acting between the member. I05 and a stationary portion I0'I of the machine.

In order to cause the beams, from the source of llight to the photocells, to follow the moving tube I 3 during the coating process, the bracket 33 is adjustably fixed to a rod I00, movable about a vertical axis in the standard 24, and pivotally carrying a lever I00, at its lower end, and connected to the lever 9i. as by 'means of pin III movable in slot II2. To deenergize the control circuits from the photocells when the plug 36" is not in engagement with the socket I4, as

well as when no envelope I0 is in position, in addition to a beli crank =lever 20 corresponding with the lever 20 of the preceding embodiment and causing contact between elements 28 and 29 in the control circuits only when an envelope I3 is in place, we provide a bracket II3 on the lever 92*, carrying an adjustable set screw II4 which causes engagement between the contacts H5 and H8 only when the plug 08" is in engagement with the socket It, thereby permitting energization of the control circuits only when there is no danger of loss of coating fluid on account of a disconnection between the flexible tube 09 and an envelope i3.

The operation of the apparatus previously described is as foliows: The conveyor II is caused to rotate continuously, bringing one tube at a time into position so that the upper end thereof lies between the source of light and the controlling photocells, the contacts 28 and 29 being engaged as the envelope reaches its position. The cam roller 90 is urged into engagement with the stationary cam 95' by spring I II, so that the lever 02 and plug 96 are carried along with the envelope I3 being coated, by engagement of the stud I03 in an aperture I04.

This causes engagement to be made between the contact elements H0 and H6, thereby permitting energization of the control circuits. During this movement of the envelope I3 with the connected llever 32 and'assooiated parts, the source of iight and control photocells follow the upper end portion 0! said envelope, because of the lever, rod, and bracket connection previously described.

The energization oi the control circuit opens the valves, corresponding with the valves 04 and I2 of the preceding embodiment, allowing coating fluid to proceed up the envelope I3- until it intercepts the light beam to the lower photocell, slowing down the action as in the first embodiment, until the light beam of the upper photocell is intercepted, whereupon the air escape valve is closed, cutting the air supply, releasing the air f above the fluid in the reservoir, and allowing said' fluid in the envelope to flow back into the reservoir through the flexible tube 00'. I

The machine is so adjusted that about this time, or shortly thereafter, the roller 04' reaches the high Part of the cam 00", causing a withdrawal of the stud I03 from the aperture I04, a deenergization of the cincuits by the disengagement oi the contacts II 0 and H5, and the snapping back of the stud I03 from the aperture I04 to engagement with the succeeding aperture I04,

under the action of return spring I00, and a repetltion oi the coating process on the next envelope.

Referring now to the embodiment of our invention illustrated in Figures 6, 'Z and 8, we illustrate portions 01' a machine which is adapted for indexing and treatment of a, plurality of envelopes I3", held in sockets I4 and supplied with coating fluid from a manifold IIO through flexible tube 09'. The construction and operation is otherwise nearly identical with that of the first embodiment. except that when coating more than one envelope at a time, provision is desirably made for the possibility that the coating fluid will rise to the top of one of the envelopes before it rises to the top of another. It is, therefore, desirable to provide means inside of the envelopes which takes care of theoverfiow of the first envelope, or envelopes, to be completely coated. and permits the fluid to rise in the remaining or last envelope, whereby all in the set are coated prior to termination of the operation In order to accomplish this result in the simultaneous coating oi, for example, three envelopes I3, we provide a stationary light source 31 and flow-retardin photocells 30, 38 and 30, one for each of said set of envelopes to be simultaneously coated, said light source and cells being so arranged with respect to the indexed.

position of the envelopes I3 that they all three receive horizontal beams of light from the source 31 through corresponding slits in the housing 30 and side or peripheral, rather than central portions, of the envelopes, thereby avoiding light.

interference due to coating on the inner tubes I28, I29 and I3I. The cells are in series with one another for a reason which parent from the description to follow.

With regard to the means for stopping the flow of coating fluid when it has reached the top of the last envelope undergoing treatment, we provide a lamp 38 whichdirects horizontal beams of light to stationary mirrors I23, I24 and I25 which, after receiving beams of light from the will become apfluid, after overflowing into the remainder of the inn 1' tubes I28, I29 and HI.

In order to prevent a coating operation when one or more of the envelopes in a. set is not in place,'the safety arrangement for the circuits controlling the valves 84 and 12*, indicated by the contacts 23?, 29 and the controlling bell crank lever 26", is duplicated for the rest of the envelopes in'a set, as indicated by the reference characters 28, 29, 28 and 29 In the present embodiment plugs 98" are moved into engagement with sockets of indexed envelopes I3", upon initiation vof the coating op eration by means of a vertical reciprocating rod I22 operated by suitable'means, such as a connecting rod I26 pivoted to a bracket I21 thereon, which bracket also adjustably carries tubes I28,

, I29 and I3I which pass through glands I32 in,

and adjustably connect with, the manifold H8 which in turn carries the plugs 98", and on through the envelopes I3 being treated, so as to not only provide an inner overflow pipe for turn connection I35 from an overflow manifold I36 to the coating fluid reservoir 61", so that said valve I34 is closed when the valve I2 is opened,

- and vice versa. Except as specifically described,

the embodiment of Figs. 6, 7 and 8 may correspond with that of Figs. 3, 4 and 5.

vThe operation of the apparatus of Figs. 6, '7 and 8 is desirably as follows: The conveyor II" is caused to rotate intermittently successively bringing, in the present mbodiment, three tubes or envelopes I3 into i exed position so that the upper ends thereof li'e horizontally between the source of light 3'I andthe cells 36, 36 and 36 while the mirrors I23, I24 and I25 similarly receive horiz ontal beams of light from the source 38", after passing through said envelopes, and reflect said light to the photocell 35 ,'as most clearly shown in Fig. 7. The contacts 28' and 29, 28 and 29, 28 and 29 engage as the envelopes index.

The connecting rod I26 movesrup the tubes I28, I29 and I3l into the indexed envelopes l3 and the plugs 96" into engagement with the sockets I4, causing engagement between; the

contact elements Ill and H", .thereby permitting energizationof the control circuits.

' overflow has taken place in two of the envelopes I3 into two of the tubes I28, I29 and HI, and the fluid rises in the slowest envelope and completely cuts oil! the light to the photocell 35 sockets N and envelopes I3", to allow said enthereby deenergizing the solenoid 19, closing velopes to pass on and another set index for a repetition of the process.

each envelope under treatment, but also allow for quicker filling and emptying due to the cor- From the foregoing it will beseen that we have provided apparatus for alternatively co'ating envelopes, such as those adapted for use in the manufacture of fluorescent lamps, whereby said envelopes are either indexed and individually coated, coated in continuous movement, or a plurality thereof are coated at one time, with or without the provision of two control valves and/or an internal overflow pipe,'and with or without an individual light source and one or two photocells for each envelope.

- Our invention provides the' following advantages over present practice:

1. The control of the coating operation is positive.

2. The control is independent of thesupply air pressure and speed of coating. v

3. The envelope being coated can be kept com-' pletely open at its upper end for speedy air escape, thereby obviating any clogging in an air outlet.

4. Labor is saved by providing automatic operation. e

5. Provision is made for adjustment for different lengths of envelope and the parts are easily replaceable.

6. Failure is guarded against by the construc- I tion of the apparatus.

-' 7. The coated envelopes may go directly to a means to hold the envelope vertically, means for automatically .feeding coating fluid thereto through its lower end, means for directing a beam of light. through its ,upper end portion, means for automatically, terminating the flow of said fluid when it intercepts saidlight beam, and

means for then automatically. withdrawing said for fee 'ngcoating fluid simultaneously to a pluralit thereof through their lower ends, means 'i'or directing a beam or light through the upper end portion of each of the envelopes, means for automatically terminating the flow of said fluid when it intercepts at least one or said light beams, and means for then automatically withdrawing said fluid.

4. Apparatus for coating the inside surfaces of light-pervious vitreous envelopes comprising means to hold the envelopes vertically, means for automatically feeding coating fluid thereto through the lower end of eachi means for directing abeam of light through a portion of said envelope adjacent but not at'its upper end, and

' another through its upperend portion, means for automatically slowing down the flow oi said fluid when it intercepts said first light beam, means extending from the coating fluid in said reservoir, means causing said tube to connect with the socket of the indexed envelope, a pipe connecting a source of compressed air to said reservoir above the coating fluid therein, a normallyclosed 'valve in said pipe for admitting or shutting oil said'compressed air and releasing the air trapped between it and said reservoir, a standard mounted adjacent the periphery oi said carrier, a photocell carried by said standard, so that it is at the level of the upper end of the indexed envelope, a source of light also carried by said standard for directing a beam horizontally on said photocell through the upper end portion of the indexed envelope, said photocell being connected to control the valve, and a switch in the valve control circuit closed only when an envelope is indexed, whereby upon indexing an envelope, said valve is opened and coating fluid forced by air pressure through the flexible tube and up into said envelope until it intercepts the light passing to the photocell, whereupon the compressed air valve is closed, the air trapped in said reservoir allowed to escape, and the coating fluid drained back into the reservoir.

6, A machine for coating the inside surfaces of light-pervious vitreous envelopes comprising a carrier with a socket for holding vertically each of a plurality of said envelopes, means for successively indexing the envelopes in said machine, a reservoir of coating fluid, a flexible tube extending from the coating fluid in said reservoir, means causing said tube to connect with the socket of the indexed envelope, a pipe connecting a source of compressed air to said reservoir above the coating fluid therein, a normallyclosed slow-up valve in said pipe for admitting or partially shutting off said compressed air, a

normally-closed shut-off valve in said pipe, nearer said reservoir, for admitting or completely shutting oil said compressed air and releasing the air trapped between it and said reservoir, a standard mounted adjacent the periphery of said carrier, 9, pair of photocells carried by said standard, so that one is at the level of the upper end of the indexed envelope and the other is lightly therebelow, a source of light also carried by said standard for directing abeam horizontally on each of said photocells through thethrough the flexible tube and up into said envelope until it intercepts the light passing to the lower photocell, whereupon the compressed air slow-up valve is closed, and the flow or coating fluid into said envelope slowed until said fluid intercepts the light to the upper photocell, whereupon the shut-ofl valve is closed. the supply of compressed air cut off, the air trapped in said reservoir allowed to escape; and the coating fluid drained back into'the reservoir.

7. A machine for coating-the inside surfaces of light-pervious vitreous envelopes comprising a carrier with a socket for holding vertically each of a plurality of said envelopes, means for rotating said carrier to move said envelopes in a circular path, a reservoir of coating fluid, a flexible tube extending from the coating fluid in said reservoir, means causing said tube to sequentially connect with one socket at a time of said envelopes, a pipe connecting a source of compressed air to said reservoir above the coating fluid, a normally closedvalve in said pipe for admitting or shutting off said compressed air and releasing the air trapped between it and said reservoir, a standard mounted adjacent the periphery of said carrier, 8. photocell carried by said standard so that it is at about the level of the upper end of the adjacent envelope, at source of light also carried by said standard for directing a beam horizontally on said'photocell through the upper end portion of said envelope, said photocell being connected to control Ithe valve, 9. switch in the valve control circuit closed only when an envelope is in position to be coated, means causing said source of light and photocell to followthe tube being coated until the operation is terminated, means then causing said flexible tube to connect with"-the socket of the next envelope and the photocell and light source to retrace for following said next envelope during its coating operation, whereby upon making a connection with an envelope said valve is opened and coating fluid forced by air pressure through the flexible tube and up into said envelope until it intercepts the light beam passing to the photocell, whereupon the compressed air valve is closed, the flow of coating fluid into the envelope terminated, the air trapped in said reservoir allowed to escape, and the coating fluid drained back into said reservoir.

. 8. A machine for coating the inside surfaces of light-pervious vitreous envelopes comprising a carrier with a socket for holding vertically each of a plurality of said envelopes, means for successively indexing simultaneously a plurality of en,-

ing fluid initially supplied to ard mounted adjacent the periphery of said car- .for directing all or said beams on said photocell,

switches in the valve control circuits closed only when the envelopes are indexed, a pipe mounted so as to lie inside of each of said envelopes and provide for draining any overflow therefrom, a

manifold connection from said pipes back to said 1 reservoir through a drain valve, and connections from said photocell to control said air and drain valves, whereby upon indexing said envelopes said compressed air valve isopened, the drain valve closed, and coating fluid forced by air pressure.

through the flexible tube and up into said envelopes until it intercepts all of the light beams passing to the photocell, whereupon the compressed air valve is closed and the drain valve opened so that the air trapped in the reservoir is allowed to escape, any coating fluid which overflows is allowed to return thereto, and the coatsaid envelopes is drained back into the reservoir. I

9. A machine for coating the inside surfaces of light-pervious vitreous envelopes comprlsing a carrier with a socket for holding vertically each of a plurality of said envelopes, means for successively indexing a plurality of said envelopes simultaneously in said machine, a reservoir of coating fluid, a flexible tube extending from the coating fluid in said reservoir, a manifold connected to said tube, means causing aid manifold to connect with the sockets oi the indexed envelopes, a pipe connecting a* source of compressed air'to said reservoir above the coating fluid therein, a normally-closed slow-up valve in said pipe for admitting or shutting 01! said compressed air, a normally-closed shut-oil! valve in said pipe, nearer said reservoir, for admitting or completely shutting-oi! said compressed air and releasing the air trapped between it and said reservoir, a pair of light sources supported so that one is at the level of the upper end of the indexed enve- 12 each of said envelopes supported at the level of the upper source of light, and another photocell supported at the level of the mirror for'receiving lightpassing through all or said envelopes from said upper source of light, said lower photocells being connected in series to control the first-mentioned valve, and the upper photocell being conwhen the envelopes are indexed, pipes to provide for draining any overflow therefrom, a manifold connection fr id P pes back to saidreservoir through a drain valve interconnected with said lopes and the other is slightly therebelow, a photocell for each of said envelopes, supported at the level of the ldwer source of light, a mirror for shut-oil valve, and means for causing said pipes to pass into and out of said envelopes to be coated as the manifold connection for coating is made or broken, whereby upon indexing said envelopes said valves are opened and coating fluid forced by air pressure through the flexible tube and'up into said envelopes until itintercepts the light passing to one of the lower photocells', where-' upon the compressed air slow-up valve is released to close and the coating fluid into said vitreous envelopes slowed down until said fluid completely intercepts the light to the upper photocell, whereupon the shut-ofl valve is closed, the drain valve opened, cutting oil. supply of compressed air, allowing the air trapped in said reservoir to escape and any coating fluid which overflows to return to, and-the fluid initially supplied to said envelopes to drain back into, the reservoir.

, ALFRED H. LAIDIG.

FREDERICK T. MAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Cohen Jan. 1. 1946 

